Various communication systems, such as microwave links, transfer data at variable data rates. For example, U.S. Patent Application Publication 2005/0075078, whose disclosure is incorporated herein by reference, describes a method for transmitting signals via a point-to-point microwave radio link. In order to improve the efficiency on the radio link, transmitted packets are classified before transmission based on quality of service parameters assigned to each packet. The signals are modulated for transmission using a real-time adaptive modulation. The modulation is adapted based on the current traffic amount, signal quality measurements indicative of the propagation conditions on the radio link, and the classification of packets comprised in the signals.
U.S. Patent Application Publication 2006/0209939, whose disclosure is incorporated herein by reference, describes a method, system and apparatus for determining a block format to be used to transmit a block of data over a channel to a receiver. The method includes collecting a series of reception-quality measurements, determining the rate of change of the reception-quality or the rate at which retransmission requests are being made, and, depending upon the magnitude of the rate of change or the rate of retransmission requests, either: averaging the lowest portion of the reception-quality measurements during the time-series and determining the block format based upon the average; or determining the block format based upon the most recent reception-quality measurements.
As another example, PCT Publication WO 2004/086668, whose disclosure is incorporated herein by reference, describes a method for transmitting and receiving data in a wireless link having a variable link quality by selecting a suitable constellation using at least an indication of the link quality and encoding the data using the selected suitable constellation.